Power circuit breakers for low voltages are known and are used to protect electric grids and the like. They have mechanically separable contact elements which are in abutment when the breaker is closed. The current to be monitored flows through the breaker and via the contact elements. An electronic trigger unit checks in each case whether a predefined current condition has been met. In the case that the current condition has been met, separation of the contact elements is triggered. A contact mechanics unit, which has a breaker shaft which is rotatably mounted about the longitudinal axis thereof, is used to separate the contact elements in the event of triggering and to switch on the breaker, that is to say to connect the contact elements which are separated from one another.
In order to supply power to the trigger unit, in each case the required electric power is drawn from the electric current flowing through the breaker by means of a current transformer, that is to say that the trigger unit has an internal power supply. It therefore draws its electric power from the grid which is intended to be protected by the power circuit breaker.
Switching to a short circuit represents the worst case for the power supply of the electronic trigger unit. The current transformer must then provide the power for the (electronics of the) trigger unit, measure and evaluate the current and generate a trigger signal in the shortest possible time. The current transformers must be appropriately configured for this case.
In the case of a DC grid, an inductive current transformer can be installed for switching to a short circuit, in order to ensure the power supply to the trigger unit.
Document DE 10 2011 083583 A1 discloses in this connection a breaker, in particular power circuit breaker for low voltages, for interrupting an electric current flowing through a conductor.
Document WO 99/14779 A1 discloses an arrangement for obtaining an auxiliary power for the operation of a trigger system of a low-voltage power circuit breaker.